Stage seals for a turbine

ABSTRACT

A plurality of ducts disposed in a stationary blade ring diaphragm of a steam turbine, the ducts have inlets disposed upstream of the last downstream fin of a labyrinth seal formed between the diaphragm and a rotor. The ducts extend through a plurality of stationary blades disposed in the diaphragm, and have outlets on the downstream side of the diaphragm adjacent a casing, for reducing the total quantity of steam bypassing the stationary and rotating blades forming one stage of the turbine by directing steam, which passes through the labyrinth seal adjacent the rotor, to an area upstream of a labyrinth seal associated with a shroud ring encircling the rotatable blades of this stage of the turbine.

llnited States Patent [1 1 Fukuda 1 STAGE SEALS FOR A TURBINE [75] Inventor: Seizi Fukuda, Nagasaki, Japan [73] Assignee: Mitsubishi Ju kogyo Kabushiki Kaisha, Tokyo, Japan [22] Filed: June 29, 1971 [21] Appl. No.: 157,900

[ 30] Foreign Application Priority Data July 11, 1970 Japan 45/60314 [52] U.S.C1 .,415/115,4l5/12l A,4l5/168, 415/010. 1 [51] Int. Cl. F04d 29/08, FOld 11/02,F01d 11/00 [58] Field of Search ..4l5/161, 121 A, DlG. 1, 415/l68,172, 116,115

[56] References Cited UNITED STATES PATENTS 935,286 9/1909 Westinghouse 415/168 2,332,322 10/1943 Kraft .1 415/168 2,848,155 8/1958 Hausmann 4l5/D1G. l

[45] July 17, 1973 FOREIGN PATENTS OR APPLICATIONS 1,013,835 12/1965 Great Britain 4l5/D1G. 1

Primary Examiner'-Henry F. Raduazo Attorney-A. T. Stratton et al.

[57] ABSTRACT A plurality of ducts disposed in a stationary blade ring diaphragm ofa steam turbine, the ducts have inlets disposed upstream of the last downstream fin of a labyrinth seal formed between the diaphragm and a rotor. The ducts extend through a plurality of stationary blades disposed in the diaphragm, and have outlets on the downstream side of the diaphragm adjacent a casing, for reducing the total quantity of steam bypassing the stationary and rotating blades forming one stage of the turbine by directing steam, which passes through the labyrinth seal adjacent the rotor, to an area upstream of a labyrinth seal associated with a shroud ring encircling the rotatable blades of this stage of the turbine.

2 Claims, 3 Drawing Figures STAGE SEALS FOR A TURBINE BACKGROUND OF THE INVENTION This invention relates to turbines and more particularly to seals between stages of the turbine.

Labyrinth seals have been used to provide a seal between rotating parts of a turbine for decades; however, they do passa small amount of fluid.

SUMMARY OF THE INVENTION In general, a turbine operable by a motive fluid flowing therethrough, when made in accordance with this invention, has an annular array of circumferentially spaced stationary blades disposed upstream of an annular array of circumferentially spaced rotatableblades, a rotor upon which the rotatable blades are mounted, and a casing encircling the blades and rotor. The annular array of stationary blades comprises at least one duct extending from. a circumferential surface adjacent the rotor, through at least one stationary blade, and then to the downstream side of the stationary blades adjacent the casing. The duct is also disposed as to allow a small portion of the motive sfluid flowing through a space between the circumferential surface and the rotor, to flow intothe duct, and throughthe duct to the downstream side of the stationaryblades adjacent the casing, and then to flow between the array of rotating blades and the casing, to reduce the total amount of motive fluid bypassing the blades and not doing useful work, thereby increasing the. efficiency of the turbine.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of this inventionwill become more apparent from reading the following detailed description in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal partial sectional view of an impulse stage of a steam turbine;

FIG. 2is a partial sectional view taken on line 1111 of FIG. 1;

FIG. 3 is a longitudinal partial sectional view of a reaction stage of a steam turbine.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, FIGS. 1 and 3 each shows a longitudinal sectional view of one stage of a steam turbine 1 having a rotor 3,.andan annular array of circumferentially spaced rotatable blades 5 mounted on the rotor 3and an annulararray of circumferentially spaced stationary nozzle blades 7 mounted in a ring diaphragm 9 encircling the rotor 3.

The ring diaphragm-9 is formed from two semicircular arcuate segments each having .an :inner and outer ring 13 and 15, respectively. The outerwring fits into a circumferential groove 16 disposed in a casing 17 encircling the rotor and blades 5 and 7.

A labyrinth seal 19 :18 disposed on the inner peripheral surface of the inner ring 13 ofthediaphragm 9 and as shown in FIGS. [and 3 comprises a gland ring 21 and a-fin 22 fastened directlyto .the diaphragm 9. The

gland "ring 21 is a segmented circular ring whichfits into a T-shaped circumferential :groove 23 .in the diaphragm ring '9 and contains a plurality 90f fins .25 extending radially inwardlyfrom the sinner pierpheralasun face thereof. The fins 25 are 'thin strips rolled the :hard

way and have an inner diameter slightly larger than the rotor 3. The rotor has a plurality of circumferential grooves27 and rings 29 which register with the fins 25 to provide a tortuous path for the steam, thus reducing the amount of steam passing between the ring diaphragm 9 and the rotor 3. Springs (not shown) bias the gland ring inwardly, so that if struck by the rotor 3 the gland ring will move outwardly to minimize damage to the labyrinth fins 25 and the rotor 3.

The rotable blades 5 are fastened to a disk wheel 31 extending radially outwardly from the rotor 3. a shroud ring 33 encircles the tips of the rotating blades providing a generally continuous ring enclosing the rotatable blades. Labyrinth stripsor fins 35 extend radially inwardly from the casing 17 and provide a labyrinth seal adjacent the casing 17 for the rotating blades.

As shown in FIGS. 1 and 3, a duct 37 has an outlet 39 adjacent the rotor and immediately upstream of the last downstream fin 22, which is fastened directly to the diaphragm ring 9. The duct 37 extends through the inner ring 13 and the stationary, blade 7, and has an outlet41 on the downstream side of the outer ring 15 and of the diaphragm ring 9, adjacent. the casing 17.

Asindieated by the arrows, a portion of the motive fluid, in this case steam, passing through the labyrinth seal 19 encircling the rotor, flows outwardly through the duct37 and across the labyrinth seal encircling the shroud ring 37. Utilizing the steam, which flows through the labyrinth seal adjacent the rotor, as the steam, which flows through the labyrinth seal adjacent the casing in each stage of the turbine, reduces the total quantity of steam, which bypasses the stationary and rotating blades in a single stage, and thus improves the general overall efficiency of the turbine. T o optimize the efiiciency, the flow through the duct 37 should substantially equal the flow through the labyrinth seal adjacent the casing 17. To equalize these flows, it is neces* sary that the pressuredrop across the stationary blades 7 be greater than the pressure drop across the rotating blades 5, as the diameters .of the two seals differ by a large amount, so that the open area in the labyrinth seal associated with the rotatingblades is much greater than the open area of the labyrinth seal 19 associated with the stationary blades, and the flow through labtrinth seals is proportional to the open area and the differential pressure across the seals. Therefore, to equalize the flow, the seal :having the smallest openarea must have the largest pressure drop. This problem is compounded, as generally large diameters require greater running clearances, thus increasing the difference in the openareas atagreater rate than the variation in diameters.

In impulse stages similar to those shown in FIG. 1, the pressure drop across the stationary blades is normally very large, and there is a very low pressure drop across the rotating blades,while in reaction stages, as shown in FIG.I3,the pressure drop across thelstationary blades may be as :high or higherthan the pressure drop across the rotating blades. Therefore, to optimize the effi- .ciency of theturbine, it would be desirable to use reaction stages in which the pressure: drop across the stationary'blades 7 is-greaterthan the pressure drop across the rotating blades .5.

FIG..2:showsthatnotall of the stationary blades have :aduct 37 extending therethrough. 1n the preferred embodiment .a plurality of ducts would .be provided in each stage, 'the :exact number .being determined by the cross sectional area of each duct 37, and the available differential pressure between areas adjacent the inlets 39 and outlets 41 of the ducts 37.

What is claimed is:

l. A steam turbine having an annular array of circumferentially spaced stationary blades disposed upstream of an annular array of circumferentially spaced rotatable blades and said stationary blades having an inner shroud ring, a rotor upon which said rotatable blades are mounted, a casing encircling said blades and rotor, and a labyrinth seal between said shroud ring and said rotor having a plurality of circumferential axially spaced fins encircling the rotor, said annular array of stationary blades having at least one duct extending from a space immediately upstream of the last downstream fin forming the labyrinth seal, radially through at least one stationary blade, and then to a downstream side of said stationary blades adjacent said casing, said duct being disposed to allow a small portion of the steam which flows through said labyrinth seal to flow into said duct, and through said duct to said downstream side of said stationary blades adjacent said casing, and then to flow between said annular array of rotatable blades and said casing to reduce the total amount of motive fluid bypassing said blades and not doing useful work, thereby increasing the efficiency of said turbine.

2. A turbine as set forth in claim 1, wherein a plurality of radial ducts extending through a plurality of stationary blades, the inlets to the ducts being disposed upstream of the last downstream circumferential fin. 

1. A steam turbine having an annular array of circumferentially spaced stationary blades disposed upstream of an annular array of circumferentially spaced rotatable blades and said stationary blades having an inner shroud ring, a rotor upon which said rotatable blades are mounted, a casing encircling said blades and rotor, and a labyrinth seal between said shroud ring and said rotor having a plurality of circumferential axially spaced fins encircling the rotor, said annular array of stationary blades having at least one duct extending from a space immediately upstream of the last downstream fin forming the labyrinth seal, radially through at least one stationary blade, and then to a downstream side of said stationary blades adjacent said casing, said duct being disposed to allow a small portion of the steam which flows through said labyrinth seal to flow into said duct, and through said duct to said downstream side of said stationary blades adjacent said casing, and then to flow between said annular array of rotatable blades and said casing to reduce the total amount of motive fluid bypassing said blades and not doing useful work, thereby increasing the efficiency of said turbine.
 2. A turbine as set forth in claim 1, wherein a plurality of radial ducts extending through a plurality of stationary blades, the inlets to the ducts being disposed upstream of the last downstream circumferential fin. 